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4" loudspeakers ( 8) I would have used the $6, 8Ω
speakers from All Electronics ( makezine.com/go/
speaker1), but they were out of stock. Instead,
I bought the 40W, 8Ω shielded woofers
( makezine.com/go/speaker2) for $8 each.
The important considerations for the speakers
are an impedance of 8Ω (which is normal for
home stereo speakers) and good frequency range
(in this case 70Hz–10KHz). Sound localization is
more acute at higher frequencies, so response
>1KHz is especially important. It would be better
to add a subwoofer to make up for thin bass
than to have no high end.
Quad spring-action speaker terminals ( 4)
makezine.com/go/terminals
Ikea Reda bowls ( 2 sets) $5 each; use the large
bowl in the set of 3 makezine.com/go/ikeabowl
Machine bolts ( 32)
Locking nuts ( 32)
Washers ( 32)
Small nuts and bolts ( 8) for the terminals. Most
of the speakers were fine with ½" bolts, but the
top and bottom ones needed longer ( 1½") ones,
as you’ll see later. This may vary, if your parts
are different.
Foam weatherstripping
Speaker wire I had some 18-gauge stuff lying around
the house; the project needs only a few feet.
TOOLS
High-speed rotary tool with #409 cutoff wheel
and #561 cutting bit
Soldering iron and solder
Heat gun and heat-shrink tubing
Wire cutters and strippers
Scissors
Pencil
Safety glasses
Earplugs It wouldn’t do to deafen yourself in the
process of building a snazzy speaker array,
would it?
both directions to ensure there aren’t any errors.
I decided to put the speakers 1" away from the
rim of the bowl. That left enough clearance to put
the lids back on. Don’t put them any farther away, or
they will whack into the top speaker inside the bowl.
4. Cut the side speaker holes.
With the Dremel cutting bit, cut along the lines you
just drew (Figure D). There is quite a bit of inaccuracy introduced by drawing a flat template onto a
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curved surface, so the first hole you cut will be too
small. Test fit the speaker, and cut out more where
it rubs against the edge. Don’t worry about ragged
edges; the speaker flange will cover them.
5. Modify the terminals.
The speaker terminals have some extra plastic that
prevents them from mounting flush to the bowl. Cut
it off using the cutoff wheel.
6. Prepare your speaker wire.
Cut a short ( 6"– 8") length of speaker wire for each
speaker. Strip the insulation about ½" back on each
end of the wires. Tin all of the ends (Figure E).
7. Solder the wires to the speakers.
It’s easier to solder the wires before attaching the
speakers to the bowl. Cut short lengths (¾") of
heat-shrink tubing and thread them on one end of
a speaker wire. Solder the ends to the speaker terminals, slide the tubing over the solder joints, and
shrink the tubing with a heat gun (Figure F).
Be sure to maintain consistent polarity. My
speaker cable has one reddish and one silver wire,
which I connect to the positive (+) and negative (-)
terminals, respectively. Other wire has colored insulation, or just a stripe on one side. Conventionally,
a red or striped wire is connected to the positive
terminal. If you are inconsistent, the speakers will
be out of phase, which will probably have no audible
effect with this system, but would be a problem with
a more scientifically calibrated setup.
8. Prepare the speakers with
weatherstripping (optional).
I ran a line of open foam weatherstripping around
the edge of all of the side speakers. (The flange of
the top speaker already sits flush against the “foot”
of the bowl.) The purpose is to fill the gap between
the speaker flange and the bowl, and hide any
messy edges.
9. Attach the speakers to the bowl.
I started this process with the top speaker. Fit the
speaker into the hole, and use a pencil to mark
where the bolts should go. Remove the speaker
and drill holes that are the same size as your bolts.
Put a washer and a locking nut on the back (see
Figure G). I used locking nuts because there will be
a lot of vibration.
